/*
 * Copyright 2008 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.cayte.create2dcode.common;

import java.util.Vector;

/**
 * <p>
 * Implements Reed-Solomon enbcoding, as the name implies.
 * </p>
 * 
 * @author Sean Owen
 * @author William Rucklidge
 */
public final class ReedSolomonEncoder {

	private final GF256 field;
	private final Vector cachedGenerators;

	public ReedSolomonEncoder(GF256 field) {
		if (!GF256.QR_CODE_FIELD.equals(field)) {
			throw new IllegalArgumentException(
					"Only QR Code is supported at this time");
		}
		this.field = field;
		this.cachedGenerators = new Vector();
		cachedGenerators.addElement(new GF256Poly(field, new int[] { 1 }));
	}

	private GF256Poly buildGenerator(int degree) {
		if (degree >= cachedGenerators.size()) {
			GF256Poly lastGenerator = (GF256Poly) cachedGenerators
					.elementAt(cachedGenerators.size() - 1);
			for (int d = cachedGenerators.size(); d <= degree; d++) {
				GF256Poly nextGenerator = lastGenerator.multiply(new GF256Poly(
						field, new int[] { 1, field.exp(d - 1) }));
				cachedGenerators.addElement(nextGenerator);
				lastGenerator = nextGenerator;
			}
		}
		return (GF256Poly) cachedGenerators.elementAt(degree);
	}

	public void encode(int[] toEncode, int ecBytes) {
		if (ecBytes == 0) {
			throw new IllegalArgumentException("No error correction bytes");
		}
		int dataBytes = toEncode.length - ecBytes;
		if (dataBytes <= 0) {
			throw new IllegalArgumentException("No data bytes provided");
		}
		GF256Poly generator = buildGenerator(ecBytes);
		int[] infoCoefficients = new int[dataBytes];
		System.arraycopy(toEncode, 0, infoCoefficients, 0, dataBytes);
		GF256Poly info = new GF256Poly(field, infoCoefficients);
		info = info.multiplyByMonomial(ecBytes, 1);
		GF256Poly remainder = info.divide(generator)[1];
		int[] coefficients = remainder.getCoefficients();
		int numZeroCoefficients = ecBytes - coefficients.length;
		for (int i = 0; i < numZeroCoefficients; i++) {
			toEncode[dataBytes + i] = 0;
		}
		System.arraycopy(coefficients, 0, toEncode, dataBytes
				+ numZeroCoefficients, coefficients.length);
	}

}
